Efficient production of hydrocarbons generally requires precise measurements of location and movement of fluids and fluid fronts in formation reservoirs. In the hydrocarbon drilling and recovery industry, many types of measurements are made to quantify fluid saturations and distribution of water, oil and gas in a reservoir. The tracking of saturation fronts is essential to the design and management of reservoir depletion strategies as well as prediction of field performance. However, determining the movement of reservoir fluids remains challenging and is addressed mainly with repeated surface geophysical measurements, including surface seismic and surface gravity data.
One challenge with using surface geophysical data is that measurement locations are far removed from the reservoir and that details of the fluid movement are smoothed by the distance from the surface observation to the fluid-fronts of interest in the reservoir. Downhole gravity measurements reduce the distance from the reservoir, but present additional challenges as measurement tools should be positioned in the same location within a well for repeat measurements.